Phytate is the major storage form of phosphorus in cereals and legumes. However, monogastric animals such as pig, poultry and fish are not able to metabolise or absorb phytate (or phytic acid) and therefore it is excreted leading to phosphorous pollution in areas of intense livestock production. Moreover phytic acid also acts as an antinutritional agent in monogastric animals by chelating metal agents such as calcium, copper and zinc.
In order to provide sufficient phosphates for growth and health of these animals, inorganic phosphate is added to their diets. Such addition can be costly and further increases pollution problems.
Phytate is converted by phytases which generally catalyse the hydrolysis of phytate to lower inositol-phosphates and inorganic phosphate. Phytases are useful as additives to animal feeds where they improve the availability of organic phosphorus to the animal and decrease phosphate pollution of the environment (Wodzinski R J, Ullah A H. Adv Appl Microbiol. 42, 263-302 (1996)).
A number of phytases of fungal (Wyss M. et al. Appl. Environ. Microbiol. 65 (2), 367-373 (1999); Berka R. M. et al. Appl. Environ. Microbiol. 64 (11), 4423-4427 (1998); Lassen S. et al. Appl. Environ. Microbiol. 67 (10), 4701-4707 (2001)) and bacterial (Greiner R. et al Arch. Biochem. Biophys. 303 (1), 107-113 (1993); Kerovuo et al. Appl. Environ. Microbiol. 64 (6), 2079-2085 (1998); Kim H. W. et al. Biotechnol. Lett. 25, 1231-1234 (2003); Greiner R. et al. Arch. Biochem. Biophys. 341 (2), 201-206 (1997); Yoon S. J. et al. Enzyme and microbial technol. 18, 449-454 (1996); Zinin N. V. et al. FEMS Microbiol. Lett. 236, 283-290 (2004))) origin have been described in the literature.
However, to date, none of these phytases display the properties required for effective use as an animal feed supplement. In particular, fungal phytases tend to be proteolytically unstable (Igbasan F. A. et al. Arch. Anim Nutr. 53, 353-373 (2000)) and therefore susceptible to degradation, while most bacterial phytases have a narrow substrate specificity for phytate alone and degrade poorly inositol phosphates of intermediate degrees of phosphorylation (Greiner R. et al., Arch. Biochem. Biophys. 303 (1), 107-113 (1993); Kerovuo J et al. Biochem. J. 352, 623-628 (2000)).
Accordingly, there is a need for improved phytases.